Devices of this type include a recessed bearing plane in the reamer head for absorbing the pressure of a clamping member against a cutter knife clamped between them, and a pair of set screws spaced apart in a pair of bore holes ending in said recessed bearing plane. These set screws are associated with the end regions of the cutter knife to move it in the direction of increased cutting diameter. Such devices also include a clamping screw which traverses a threaded hole in the reamer head and a hole in the clamping member or clamping shoe and, with its head seated in the clamping member, presses the clamping member against a first side of the hard metal cutter knife.
Devices of this kind have become known, for example, from the German Pat. No. 1,144,568, the U.S. Pat. No. 3,490,315 and particularly from the German Pat. No. 1,427,182, FIGS. 1-3.
The latter has practically dominated the market but has had the following shortcomings:
(a) Hard-metal knives have many properties in common with those of glass: they shatter easily and the fracture sites have very sharp edges. When such a hard-metal knife fractures, notches are formed at the bearing points in the head which represent roughnesses. As a result, the entire machine reamer made of expensive special steel has to be discarded.
(b) When the hard-metal knive is set for a smaller diameter, then the bearing surface of the hard-metal knife is larger and becomes smaller the larger the diameter. This, however, is undesirable since it is obvious that at larger diameters, larger forces are introduced into the hard-metal knife than at smaller diameters.
(c) When the hard-metal knife is set for a smaller diameter, then the clamping member is situated more in the direction of the center portion of the hard-metal knife than when the hard-metal knife is set for larger diameters. This means that the manner in which forces are introduced and absorbed is also affected from this side.
(d) The setscrews press via wedge-shaped pieces against the free surfaces of the inside edge of the hard-metal knife. This means the introduction of different forces into the hard-metal knife. In order to be at all able to absorb these forces, it must be relatively wide. However, at the high cost of hard-metal, this means a wasting of material. In addition, great care must be taken by accurate manufacture so that forces are not introduced directly at the cutting edges because the latter would then simply break away.
(e) The hard-metal knife must, therefore, withstand opposing forces: it must, on the one hand, be gripped with great force, but at the same time, it must still be amenable to a radial displacement.
(f) In order to keep the difference of the forces occuring at different radii from becoming excessive, only a small range of diameters can be covered with one machine reamer. It is, therefore, necessary to keep a relatively large number of machine reamer sizes in stock.